Electrical resistometry study of an AlMgSi alloy under artificial aging

The artificial aging of an AlMgSi commercial alloy was studied by electrical resistometry measurements. A laboratory-made experimental arrangement was designed in order to avoid natural aging prior to artificial aging. The electrical resistometry evolution was compared to Vickers microhardness determinations, and correlated with the precipitation sequence. The temporal evolution of β″ relative volume fraction is described by a normalized resistance evolution by means of a Johnson-Mehl-Avrami type equation. The activation energy is in good agreement with that obtained from differential scanning calorimetric experiments.Fil: Stipcich, Marcelo Fernando. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Cuniberti, Adela Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Noseda Grau, Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentin

El estudio de las piezas de artillería del fuerte independencia (Ciudad de Tandil, provincia de Buenos Aires)

Los cañones del Fuerte Independencia (1823), funcionaron como bastión defensivo frente al ingreso de ejércitos de potencias extranjeras. Este patrimonio incluye seis cañones fabricados con una aleación de base de hierro con diferentes tipos de sellos grabados en bajo y sobre relieve. Se posee escasa información sobre su historia inicial y de sus traslados hacia al interior de la región pampeana por parte del general Martín Rodríguez. Se poseen pocos datos sobre el uso de estas piezas en la fortificación. En este trabajo se presentan los resultados del análisis de dos de los cañones: sus marcas de fábrica, usos previos y posteriores a la fundación del fuerte, determinación de los materiales que se encontraron en su interior y datos relacionados con fuentes documentales. En la actualidad estas piezas se encuentran ubicadas en el Museo Histórico del Fuerte Independencia de Tandil (MUHFIT) y en el Parque Independencia; este último, fue colocado en ese lugar en ocasión de festejarse el centenario de la ciudad (1923). Los datos recopilados de la estructura del cañón, huellas o indicios de fabricación, materiales utilizados, análisis de su microestructura, objetos encontrados en el ánima de uno de los cañones aportan información sobre sus características interna y externa que permiten reconstruir la historia de estas piezas. Simultáneamente se recopiló información documental sobre el uso de estos artefactos en la zona, determinando su funcionalidad tanto con las comunidades originarias como en distintos contextos políticos del siglo XIX

Avalanche criticality in the martensitic transition of Cu67.64Zn16.71Al15.65 shape-memory alloy: a calorimetric and acoustic emission study

The first-order diffusionless structural transition in Cu67.64Zn16.71Al15.65 is characterized by jerky propagation of phase fronts related to the appearance of avalanches. In this paper, we describe a full analysis of this avalanche behavior using calorimetric heat-flux measurements and acoustic emission measurements. Two different propagation modes, namely, smooth front propagation and jerky avalanches, were observed in extremely slow measurements with heating and cooling rates as low as a few 10−3 K/h. Avalanches show criticality where each avalanche leads to a spike in the heat flux. Their statistical analysis leads to a power law [P(E)∼E−ε, where P(E)dE is the probability to observe an avalanche with energy E in an interval between E and E+dE] with an energy exponent of ε=2.15±0.15 in excellent agreement with the results of acoustic emission measurements. Avalanches appear to be more common for heating rates faster than 5×10−3 K/h whereas smooth front propagation occurs in all calorimetric measurements and (almost) exclusively for slower heating rates. Repeated cooling runs were taken after a waiting time of 1 month (and an intermediate heating run). Correlations between the avalanche sequences of the two cooling runs were found for the strongest avalanche peaks but not for the full sequence of avalanches. The memory effect is hence limited to strong avalanches

Avalanche criticalities and elastic and calorimetric anomalies of the transition from cubic Cu-Al-Ni to a mixture of18Rand2Hstructures

We studied the two-step martensitic transition of a Cu-Al-Ni shape-memory alloy by calorimetry, acoustic emission (AE), and resonant ultrasound spectroscopy (RUS) measurements. The transition occurs under cooling from the cubic (β, Fm3m) parent phase near 242 K to a mixture of orthorhombic 2H and monoclinic 18R phases. Heating leads first to the back transformation of small 18R domains to β and/or 2H near 255 K, and then to the transformation 2H to β near 280 K. The total transformation enthalpy is ΔHT=328±10 J/mol and is observed as one large latent heat peak under cooling. The back-transformation entropy under heating breaks down into a large component 18R to β at 255 K and a smaller, smeared component of the transformation 2H to β near 280 K. The proportions inside the phase mixture depend on the thermal history of the sample. The elastic response of the sample is dominated by large elastic softening during cooling. The weakening of the elastic shear modulus shows a peak at 242 K, which is typical for the formation of complex microstructures. Cooling the sample further leads to additional changes of the microstructure and domain wall freezing, which is seen by gradual elastic hardening and increasing damping of the RUS signal. Heating from 220 K to room temperature leads to elastic anomalies due to the initial transformation, which is now shifted to high temperatures. The transition is smeared over a wider temperature interval and shows strong elastic damping. The shear modulus of the cubic phase is recovered at 280 K. The phase transformation leads to avalanches, which were recorded by AE and by time-resolved calorimetry. The cooling transition shows very extended avalanche signals in calorimetry with power-law distributions. Cooling and heating runs show AE signals over a large temperature interval above 260 K. Splitting the transformation into two martensite phases leads to power-law exponents ɛ∼2 (β↔ 18R) and ɛ∼1.5 (β↔ 2H) while the phase mixture shows an effective AE exponent of 1.7

Caloric effects induced by magnetic and mechanical fields in a Ni50Mn25-xGa25Cox magnetic shape memory alloy

"We have studied the elastocaloric effect in a Co-doped Ni-Mn-Ga magnetic Heusler shape memory alloy in the vicinity of its martensitic transition. Measurements of the length change as a function of temperature have been carried out across the transition under applied compression stresses and magnetic fields. The isothermal stress-induced entropy changes have been computed from the experimental data. Results evidence a significant elastocaloric effect associated with the large entropy change of the structural phase transition. The alloy also exhibits a magnetocaloric effect at low applied magnetic fields. It is shown that application of a magnetic field below 1 T increases the estimated elastocaloric relative cooling power by about 20%. A comparison of elasto-and magnetocaloric properties indicates that a similar relative cooling power is reached under application of 10 MPa or 0.8 T.

Cuerpo rígido: experiencia de laboratório con material de bajo costo

Con este trabajo, se pretende revalorizar la utilidad de las experiencias de bajo costo en cursos de Física básica universitaria. Se analiza una experiencia de laboratorio que tiene como objetivo caracterizar el movimiento de una esfera, en un plano inclinado, mediante dos enfoques diferentes: desde el punto de vista cinemático como movimiento uniformemente acelerado y desde el punto de vista de la dinámica rotacional, es decir, considerando a las esferas como masas puntuales o sólidos rígidos. El aspecto más interesante, desde el punto de vista de la riqueza conceptual del análisis, es la reformulación de las clásicas ecuaciones que se utilizan para resolver el problema tomando en cuenta que la esfera rototraslaciona en una canaleta apoyando en dos puntos

Low-temperature entropy in Cu-based shape-memory alloys and its relation to the boson peak

Cu-based shape-memory alloys display an (open) bcc phase or B phase at high temperature, and transform martensitically towards a close-packed structure at a lower temperature..

Effect of Ag addition on the martensitic phase of the Cu-10 wt.% Al alloy

Thermal analysis and compression tests at room temperature have been carried out for Cu-10 wt.% Al and Cu-10 wt.% Al-10 wt.% Ag alloys samples. The results indicate that the decomposition reaction of the (β1) parent phase is decreased suppressed and a martensite stabilization effect can be induced by Ag addition. The Cu-Al-Ag alloy shows some degree of shape memory capacity.Fil: Silva, R.A.G.. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Cuniberti, Adela Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Stipcich, Marcelo Fernando. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física de Materiales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil; ArgentinaFil: Adorno, A.T.. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi